1. Science Department, SUNY Maritime College, 6 Pennyfield Av., Throggs Neck, NY 10465, USA
2. Faculty of Physics, University of Warsaw, Pasteura 5, PL-02-093 Warsaw, Poland
3. Center for Theoretical Physics of PAS, Al. Lotników 32/46, PL-02-688 Warsaw, Poland
4. Mathematical Institute, Oxford University, Radcliffe Observatory Quarter, Woodstock Rd., Oxford OX2 6GG, UK